U.S. Pat. No. 7,552,586, the disclosure of which is incorporated herein by reference, discloses a marine exhaust system having an oxygen sensor located within a catalyst housing structure and downstream of a catalyst device. The oxygen sensor is located away from a reversion liquid trajectory path that defines the likely path of liquid flowing in a reverse direction through the marine engine exhaust system toward a plurality of exhaust ports of the engine. By locating the engine sensor away from this reversion liquid trajectory path, the likelihood of damage to the oxygen sensor from contact with liquid is significantly reduced.
U.S. Pat. No. 7,698,889, the disclosure of which is incorporated herein by reference, discloses a porous member disposed within the exhaust stream of a marine engine at a location where its temperature approximates the temperature of the exhaust stream through normal use of the engine. Exhaust gas flows freely through the non-catalytic porous member, but liquid passing in a reverse direction through the exhaust system is vaporized as it attempts to flow through the non-catalytic porous member.
U.S. Patent Application Publication No. 2011/0039461, the disclosure of which is incorporated herein by reference, discloses a plenum provided upstream from a catalyst module and downstream from a plurality of exhaust ports of a marine engine. The plenum is provided with a cross-sectional area that induces exhaust gas to slow as it passes from the plurality of exhaust ports into the plenum. This slowing of the velocity of exhaust gas improves the probability that the exhaust gas will be more evenly distributed across the inlet surface of the catalyst module.